fix(growth): 穷尽审计修复 — tracker timeline 断链 + 文档更新

P1-1: tracker.rs record_learning 改为通过 MemoryEntry 存储
      (之前用 store_metadata 存但 get_timeline 用 find_by_prefix 读，
       两条路径不交叉，timeline 永远返回空)

P2-4: extractor.rs 移除未使用的 _llm_driver 绑定，改为 is_none() 检查

P2-5: lib.rs 模块文档更新，反映实际 17 个模块而非原始 4 个

profile_updater.rs: 添加注释说明只收集 update_field 支持的字段

测试: zclaw-growth 137 tests, zclaw-runtime 87 tests, 0 failures

crates/zclaw-growth/src/tracker.rs

@@ -66,21 +66,30 @@ impl GrowthTracker {
             timestamp: Utc::now(),
         };
 
-        // Store learning event
-        self.viking
-            .store_metadata(
-                &format!("agent://{}/events/{}", agent_id, session_id),
-                &event,
-            )
-            .await?;
+        // Store learning event as MemoryEntry so get_timeline can find it via find_by_prefix
+        let event_uri = format!("agent://{}/events/{}", agent_id, session_id);
+        let content = serde_json::to_string(&event)?;
+        let entry = crate::types::MemoryEntry {
+            uri: event_uri,
+            memory_type: MemoryType::Session,
+            content,
+            keywords: vec![agent_id.to_string(), session_id.to_string()],
+            importance: 5,
+            access_count: 0,
+            created_at: event.timestamp,
+            last_accessed: event.timestamp,
+            overview: None,
+            abstract_summary: None,
+        };
+        self.viking.store(&entry).await?;
 
-        // Update last learning time
+        // Update last learning time via metadata
         self.viking
             .store_metadata(
                 &format!("agent://{}", agent_id),
                 &AgentMetadata {
                     last_learning_time: Some(Utc::now()),
-                    total_learning_events: None, // Will be computed
+                    total_learning_events: None,
                 },
             )
             .await?;